Topological insulator based spin torque oscillator reader

ABSTRACT

The present disclosure generally relates to a bismuth antimony (BiSb) based STO (spin torque oscillator) sensor. The STO sensor comprises a SOT device and a magnetic tunnel junction (MTJ) structure. By utilizing a BiSb layer within the SOT device, a larger spin Hall angle (SHA) can be achieved, thereby improving the efficiency and reliability of the STO sensor.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

Embodiments of the present disclosure generally relate to a spin torqueoscillator (STO) sensor having a spin-orbit torque (SOT) devicecomprising a topological insulator of bismuth antimony (BiSb) and amagnetic tunnel junction (MTJ) structure.

Description of the Related Art

Spin-transfer torque (STT) based spin torque oscillator (STO) deviceshave been proposed as a read element in hard disk drives (HDD). STOdevices detect the spin torque induced magnetic free layerprecession/oscillation in the frequency domain. However, STT based STOdevices are two-terminal devices and generally require a current to flowperpendicularly through the device. As such, a higher applied current isneeded in order to achieve a high signal/frequency output. This highercurrent is not ideal for reliability concerns. As such, spin-orbittorque (SOT) based 3-terminal STO devices are preferred because, in SOTbased STO devices, magnetic layer processing/oscillation is induced byan in-plane current that flows through the SOT layer by the spin Halleffect. At the same time, the signal (frequency) detected is done usinga separate current perpendicular to plane (CPP) read current path.Therefore, a large current is not needed. This configuration can providebetter device reliability. However, conventional SOT-based STO devicesgenerally induce less precession/oscillation, hence lower signal outputand smaller dynamic frequency range due to a low efficiency from asmaller spin Hall angle (SHA).

Bismuth antimony (BiSb) is a material that has been proposed as a SOTlayer for various SOT device applications, such as for energy-assistedmagnetic recording (EAMR) write heads. BiSb layers are narrow bandgaptopological insulators with both giant spin Hall effect and highelectrical conductivity.

Therefore, an improved SOT device is needed to utilize a BiSb layer withimproved spin Hall angle and efficiency as STO nano-oscillator in HDDreader sensors.

SUMMARY OF THE DISCLOSURE

The present disclosure generally relates to a bismuth antimony (BiSb)based STO (spin torque oscillator) sensor. The STO sensor comprises aSOT device and a magnetic tunnel junction (MTJ) structure. By utilizinga BiSb layer within the SOT device, a larger spin Hall angle (SHA) canbe achieved, thereby improving the efficiency and reliability of the STOsensor.

In one embodiment, a sensor comprises: a seed layer; a bismuth antimony(BiSb) layer disposed over the seed layer; a buffer layer disposed overthe BiSb layer; an magnetic tunnel junction (MTJ) structure disposedover the buffer layer, wherein the seed layer, the BiSb layer, thebuffer layer, and the MTJ structure are disposed at a media facingsurface (MFS); and an antiferromagnetic (AFM) layer.

In another embodiment, a sensor comprises: a seed layer; a magnetictunnel junction (MTJ) structure disposed over the seed layer; a firstbuffer layer disposed over the MTJ structure; a bismuth antimony (BiSb)layer disposed over the first buffer layer; a second buffer layerdisposed over the BiSb layer; a capping layer disposed over the secondbuffer layer; wherein the seed layer, the MTJ structure, the firstbuffer layer, the BiSb layer, the second buffer layer, and the cappinglayer are disposed at a media facing surface (MFS); and anantiferromagnetic (AFM) layer, wherein the AFM is disposed between theseed layer and the capping layer.

In yet another embodiment, a sensor comprises: a bismuth antimony (BiSb)layer having a (012) orientation; a free layer; a MgO layer; a pinninglayer; a capping layer; an antiferromagnetic (AFM) layer; and a biaslayer disposed at a media facing surface (MFS).

In another embodiment, a method of using a magnetic recording headcomprises: flowing a current through a spin orbit torque (SOT) device ofa spin torque oscillator (STO) sensor while reading data from a magneticrecording media; and measuring frequency of a precession of the a freelayer in the STO sensor, wherein the precession is responsive to amagnetic field generated by the magnetic recording media.

BRIEF DESCRIPTION OF THE DRAWINGS

So that how the above-recited features of the present disclosure can beunderstood in detail, a more particular description of the disclosure,briefly summarized above, may be had by reference to embodiments, someof which are illustrated in the appended drawings. However, it is to benoted that the appended drawings illustrate only typical embodiments ofthe disclosure and are therefore not to be considered limiting of itsscope, for the disclosure may admit to other equally effectiveembodiments.

FIG. 1 is a schematic illustration of certain embodiments of a magneticmedia drive, including an STO read head having a SOT device.

FIG. 2 is a fragmented, cross-sectional side view of certain embodimentsof a read head having a SOT based STO sensor.

FIGS. 3A and 3B illustrate applied magnetic field vs. frequency forvarious SOT based STO sensors.

FIG. 4A illustrates a BiSb based STO device according to one embodiment.

FIGS. 4B-4E illustrate various views of a top pinned BiSb based sensoraccording to various embodiments.

FIG. 5A illustrates a BiSb based STO device according to one embodiment.

FIGS. 5B-5E illustrate various views of a bottom pinned BiSb basedsensor according to various embodiments.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may benefit from other embodiments without specificrecitation.

DETAILED DESCRIPTION

In the following, reference is made to embodiments of the disclosure.However, it should be understood that the disclosure is not limited tospecifically described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practice thedisclosure. Furthermore, although embodiments of the disclosure mayachieve advantages over other possible solutions and/or over the priorart, whether or not a given embodiment achieves a particular advantageis not limiting the disclosure. Thus, the following aspects, features,embodiments, and advantages are merely illustrative and are notconsidered elements or limitations of the appended claims except whereexplicitly recited in a claim(s). Likewise, reference to “thedisclosure” shall not be construed as a generalization of any inventivesubject matter disclosed herein and shall not be considered to be anelement or limitation of the appended claims except where explicitlyrecited in a claim(s).

The present disclosure generally relates to a bismuth antimony (BiSb)based STO (spin torque oscillator) sensor. The STO sensor comprises aSOT device and a magnetic tunnel junction (MTJ) structure. The SOTdevice comprises a bismuth antimony (BiSb) layer having a thickness ofabout 5 nm to about 10 nm. By utilizing a BiSb layer within the SOTdevice, a larger spin Hall angle (SHA) can be achieved, therebyimproving the efficiency and reliability of the STO sensor.

A BiSb layer having a (012) orientation has a significant spin Hallangle and high electrical conductivity. Therefore, a BiSb layer having a(012) orientation can form a SOT device. For example, a BiSb layerhaving a (012) orientation can be used as a spin Hall layer in a SOTdevice in a magnetic recording head, e.g., as part of a write head suchas a MAMR write head. In another example, a BiSb layer having a (012)orientation can be used in nano oscillator devices for reading headapplications where a signal is detected in the frequency domain. The SOTdevice can be in a perpendicular stack configuration or an in-planestack configuration. The SOT device can be utilized in, for example,write heads, read heads, nano-oscillator based readers, artificialintelligence chips, and other applications. A BiSb layer stack with a(012) orientation has a higher spin Hall angle and higher performance ina SOT device than a BiSb layer with a (001) orientation.

FIG. 1 is a schematic illustration of certain embodiments of a magneticmedia drive 100. Such a magnetic media drive may be a single drive orcomprise multiple drives. For the sake of illustration, a single diskdrive is shown according to certain embodiments. As shown, at least onerotatable magnetic disk 112 is supported on a spindle 114 and rotated bya drive motor 118. The magnetic recording on each magnetic disk 112 isin the form of any suitable patterns of data tracks, such as annularpatterns of concentric data tracks (not shown) on the magnetic disk 112.

At least one slider 113 is positioned near the magnetic disk 112. Eachslider 113 supports one or more magnetic head assemblies 121, includinga STO device. As the magnetic disk 112 rotates, the slider 113 movesradially in and out over the disk surface 122. The magnetic headassembly 121 may access different tracks of the magnetic disk 112 wheredesired data are written. Each slider 113 is attached to an actuator arm119 using a suspension 115. The suspension 115 provides a slight springforce which biases the slider 113 toward the disk surface 122. Eachactuator arm 119 is attached to an actuator means 127. The actuatormeans 127, as shown in FIG. 1 , maybe a voice coil motor (VCM). The VCMincludes a coil movable within a fixed magnetic field, the direction,and speed of the coil movements being controlled by the motor currentsignals supplied by the control unit 129.

During operation of the disk drive 100, the rotation of the magneticdisk 112 generates an air bearing between the slider 113 and the disksurface 122 which exerts an upward force or lift on the slider 113. Theair bearing thus counter-balances the slight spring force of suspension115. In addition, it supports the slider 113 off and slightly above thedisk surface 122 by a small, substantially constant spacing duringregular operation.

The various components of the disk drive 100 are controlled in operationby control signals generated by the control unit 129, such as accesscontrol signals and internal clock signals. Typically, the control unit129 comprises logic control circuits, storage means, and one or moremicroprocessors. The control unit 129 generates control signals tocontrol various system operations, such as drive motor control signalson line 123 and head position, and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position the slider 113 to the desired data track ondisk 112. In addition, write and read signals are communicated to andfrom write and read heads on the magnetic head assembly 121 by way ofrecording channel 125.

The above description of a typical magnetic media drive and theaccompanying illustration of FIG. 1 are for representation purposesonly. However, it should be apparent that magnetic media drives maycontain many media, or disks and actuators, and each actuator maysupport several sliders.

It is to be understood that the embodiments discussed herein areapplicable to a data storage device such as a hard disk drive (HDD) aswell as a tape drive such as a tape embedded drive (TED) or aninsertable tape media drive, such as those conforming to the LTO (LinearTape Open) standards. An example TED is described in U.S. Pat. No.10,991,390, issued Apr. 27, 2021, titled “Tape Embedded Drive,” andassigned to the same assignee of this application, which is hereinincorporated by reference. As such, any reference in the detaileddescription to an HDD or tape drive is merely for exemplificationpurposes and is not intended to limit the disclosure unless explicitlyclaimed. For example, references to disk media in an HDD embodiment areprovided as examples only, and can be substituted with tape media in atape drive embodiment. Furthermore, reference to or claims directed tomagnetic recording devices or data storage devices are intended toinclude at least both HDD and tape drive unless HDD or tape drivedevices are explicitly claimed.

FIG. 2 is a fragmented, cross-sectional side view of certain embodimentsof a recording head 200 having an STO sensor. The recording head 200faces a magnetic disk 112. The recording head 200 may correspond to themagnetic head assembly 121 described in FIG. 1 . In addition, therecording head 200 includes a media-facing surface (MFS) 212, such as agas-bearing surface, facing disk 112, a magnetic write head 210, and anSTO read head 211. As shown in FIG. 2 , the magnetic disk 112 moves pastthe magnetic write head 210 in the direction indicated by the arrow 232,and the recording head 200 moves in the direction indicated by arrow234.

The magnetic write head 210 includes a main pole 220, a leading shield206, a trailing shield 240, and a coil 218 that excites the main pole220. The coil 218 may have a “pancake” structure that winds around aback-contact between the main pole 220 and the trailing shield 240,instead of a “helical” structure shown in FIG. 2 . The main pole 220includes a trailing taper 242 and a leading taper 244. The trailingtaper 242 extends from a location recessed from the MFS 212 to the MFS212. The leading taper 244 extends from an area suspended from the MFS212 to the MFS 212. The trailing taper 242 and the leading taper 244 mayhave the same degree of taper, and the degree of taper is measuredconcerning a longitudinal axis 260 of the main pole 220. In someembodiments, the main pole 220 does not include the trailing taper 242and the leading taper 244. Instead, the main pole 220 has a trailingside (not shown) and a leading side (not shown), and the trailing sideand the leading side are substantially parallel. The main pole 220 maybe a magnetic material, such as a FeCo alloy. The leading shield 206 andthe trailing shield 240 may be a magnetic material, such as a NiFealloy. In certain embodiments, the trailing shield 240 can include atrailing shield hot seed layer 241. The trailing shield hot seed layer241 can consist of a high moment sputter material, such as CoFeN orFeXN, where X comprises Rh, Al, Ta, Zr, and Ti. The trailing shield 240does not have a trailing shield hot seed layer in certain embodiments.

In some embodiments, the read head 211 is an STO read head or readerwith an STO sensing element 204 located between shields S1 and S2. Themagnetic fields of the adjacent magnetized regions in the magnetic disk112 are detectable by the STO sensing element 204 as the recorded bits.In STO sensing elements 204 comprising a BiSb layer, such as the SOTdevices described in FIGS. 4A-4D and 5A-5D, the STO reader may beoperated in a 2-terminal or a 3-terminal configuration, with an in-planecurrent flowing inside the SOT (the BiSb layer in this case) devicewhile a small sensing current flows perpendicular to the film plane, andthe signal is read out by measuring the frequency of magnetic layerprecession. The SOT device of various embodiments can be incorporatedinto the read head 211.

FIGS. 3A and 3B illustrate oscillator frequency vs. applied magneticfield (mimic media field (Happ (Oe))) for various oscillator devices.FIG. 3A illustrates a relationship between the applied magnetic field(Happ (Oe)) vs. detected oscillating frequency (f0 (Gz)) for aconventional STO device and for a BiSb based STO device. ConventionalSTO based devices typically have a smaller spin Hall angle (SHA) ascompared to BiSb based STO devices under the same input current density.For example, here both the conventional STO device and the BiSb basedSTO device have an input of inplane current density of J=4×10⁷ A/cm².The conventional STO device has a SHA of 0.4, whereas the BiSb based STOdevice has a SHA of 2. It can also been seen that as the appliedmagnetic field is increased, the performance of the conventional STOdevice suffers because a high frequency cannot be achieved. Thus, forconventional STO devices, because of smaller SHA (here, 0.4), thedetected field range will be smaller. Furthermore, signal sensitivity,measured as slope of curve, can be poor. A conventional STO device witha SHA˜0.4 has a sensitivity of about 40 GHz/T, just marginally largerthan gyromagnetic ratio ˜28 GHz/T. However, in a BiSb based STO devicewith a SHA of 2, the linear relationship between detected frequency andthe applied magnetic field is expanded in a larger dynamic range.Furthermore, STO signal sensitivity can reach ˜100 GHz/T, which is atleast twice larger than conventional STO device. As such, a reader basedon such a BiSb based STO device has a high performance.

FIG. 3B illustrates a relationship between the applied magnetic field(mimic media field (Happ (Oe))) to detected oscillating frequency (f0(Gz)) for a BiSb based oscillator device having an SHA of 2, at acurrent density of J=2×10⁷ A/cm² and 4×10⁷ A/cm². Although, the BiSbbased STO device at a J=4×10⁷ A/cm² exhibits a slightly larger frequencythan the BiSb based STO device with a J=2×10⁷ A/cm², the BiSb based STOdevice with J=2×10⁷ A/cm² still maintains a linear relationship betweenthe applied magnetic field and the frequency and minimal slope (signaldetection sensitivity) difference. As such, the reliability of a BiSbbased STO device at a J=2×10⁷ A/cm² is improved compared to a BiSb basedSTO device at a J=4×10⁷ A/cm² because a lower current can be used whilestill maintaining the desired performance. Therefore, the followingembodiments focus on various BiSb based STO sensors.

FIG. 4A illustrates a BiSb based STO stack 400 according to oneembodiment. The stack 400 may be used in the read head of the disk drive100 of FIG. 1 , the read head 211 of FIG. 2 , or other suitable magneticmedia drives.

The stack 400 comprises a first shield 410 a, a seed layer 412 disposedover and in contact with the first shield 410 a, a SOT device 417disposed over and in contact with the seed layer 412, a magnetic tunneljunction (MTJ) structure 418 disposed over and in contact with the SOTdevice 417, a capping layer 420 disposed over and in contact with theMTJ structure 418, and a second shield 410 b disposed over and incontact with the capping layer 420. The seed layer 412 may comprise oneor more sublayers (not shown). The SOT device 417 comprises a BiSb layer414 disposed over the seed layer 412 and a buffer layer 416 disposedover the BiSb layer 414. The MTJ structure 418 comprises a free layer(FL) 418 a disposed over the buffer layer 416, an insulation layer(tunnel barrier) such as MgO 418 b disposed over the FL 418 a, and apinning layer 418 c disposed over the insulation layer 418 b, whereinthe pinning layer 418 c comprises one or more sublayers (not shown).

The first shield 410 a is comprised of a magnetic material such as NiFe.The second shield 410 b is comprised of the same material as the firstshield 410 a. The seed layer 412 comprises a material selected from agroup consisting of NiFeTa, RuAl, Ti, CoFeB, MgO, CrMo, Cr, NiCu, NiFe,NiAl, and combinations thereof. Example configurations of the seed layer412 may include: NiFeTa/RuAl, Ti/CoFeB/MgO, CrMo, heated (e.g., attemperature 200° C.-400° C.) deposited Cr, and MgO/NiCu/NiFe (as used inthis disclosure, a “/” is used to denote separate layers in a multilayerstructure). The composition of the seed layer is chosen to enhance the[012] texture of the BiSb layer 414 such that the desired high SHA isachieved and correspondingly, Sb diffusion is minimized. As a result,the BiSb layer 414 may have a (012) crystal orientation. The bufferlayer 416 comprises a material selected from the group consisting ofNiOx, Ru, and combinations thereof. The composition of the buffer layer416 is chosen to enhance the spin transmission from the BiSb layer 414to the MTJ structure 418 and reduce direct current shunting. The FL 418a comprises a material selected from the group consisting of CoFeB, Co,CoFe, CoHf, NiFe, and combinations. The insulation layer 418 b may beformed of MgO. The pinning layer 418 c includes syntheticantiferromagnetic structures (SAF): a first ferromagnetic layer (FM1)/aRu layer/a second ferromagnetic layer (FM2), where FM1 and FM2 arematerials selected from the group consisting of CoFe, CoFeB, NiFe, andcombinations thereof. The capping layer 420 comprises a materialselected from the group consisting of, NiFeTa, NiTa, NiW, NiFeW, CoHf,CoFeHf, Pt, NiCu, CoCu, Ru, Ta, Cr, Au, Rh, other non-magneticmaterials, and combinations thereof.

In embodiments where the seed layer 412 comprises Ti/CoFeB/MgO, the Tisublayer has a thickness (not shown) in the y-direction of about 20angstroms (Å), the CoFeB sublayer has a thickness (not shown) in they-direction of about 5 Å, and the MgO sublayer has a thickness (notshown) in the y-direction of about 20 Å. Thus, in embodiments where theseed layer 412 comprises Ti/CoFeB/MgO, the seed layer 412 has a firstthickness 440 in the y-direction of about 45 Å. In embodiments where theseed layer 412 comprises CrMo, or Cr, the seed layer 412 has a firstthickness 440 in the y-direction of about 30 Å. The BiSb layer 414 has asecond thickness 442 in the y-direction of about 5 nanometers (nm) toabout 10 nm, wherein the thickness is configured to maintain desiredsurface conductivity and bulk insulation properties. In embodimentswhere the buffer layer 416 comprises NiOx, the buffer layer 416 has athird thickness 444 in the y-direction of about 0.5 nm to about 2 nm.

FIG. 4B illustrates an MFS view of a sensor 402 according to oneembodiment. The sensor 402 is a BiSb based STO device. The sensor 402may comprise the stack 400 of FIG. 4A. The sensor 402 may be used in theread head of the disk drive 100 of FIG. 1 , the read head 211 of FIG. 2, or other suitable magnetic media drives.

The sensor 402 comprises a first shield 410 a, a seed layer 412 disposedadjacent to and in contact with the first shield 410 a, a BiSb layer 414adjacent to and in contact with the seed layer 412, a buffer layer 416adjacent to and in contact with the BiSb layer 414, a MTJ structure 418adjacent to and in contact with the buffer layer 416, a capping layer420 disposed adjacent to and in contact with the MTJ structure 418, anda second shield 410 b disposed adjacent to and in contact with thecapping layer 420. The sensor 402 further comprises a first bias 430 a,and a second bias 430 b, wherein the first and second bias 430 a, 430 b,are disposed adjacent to the buffer layer 416, the MTJ structure 418,and the capping layer 420, wherein a first insulation layer 415 aseparates the first bias 430 a from the buffer layer 416, the MTJstructure 418, and the capping layer 420, and a second insulation layer415 b separates the second bias 430 b from the buffer layer 416, the MTJstructure 418, and the capping layer 420 (i.e. the buffer layer 416, theMTJ structure 418, and the capping layer 420 are disposed between thefirst bias 430 a and the second bias 430 b in the x-direction). Thefirst and second bias 430 a, 430 b are further disposed in between theBiSb layer 414 and the second shield 410 b in the y-direction.

The first shield 410 a, the second shield 410 b, the seed layer 412, theBiSb layer 414, the buffer layer 416, and the MTJ structure 418 may becomprised of the same materials described in FIG. 4A. The first bias 430a may be a hard or soft bias. The second bias 430 b comprises the samematerial as the first bias 430 a. In embodiments where the first andsecond bias 430 a, 430 b are soft bias, the first and second bias 430 a,430 b may contact the second shield 410 b, as shown in FIG. 4B. Inembodiments where the first and second bias 430 a, 430 b are hard bias,the first insulation layer 415 a may further separate the first bias 430a from the second shield 410 b, and the second insulation layer 415 bmay further separate the second bias 430 b from the second shield 410 b(i.e. the first and second bias do not contact the second shield 410 b).

FIG. 4C illustrates a cross-section of a sensor 404 according to oneembodiment. The sensor 404 is a top pinned BiSb based STO device. Thesensor 404 may be the sensor 402 of FIG. 4B. The sensor 404 may comprisethe stack 400 of FIG. 4A. The sensor 404 may be used in the read head ofthe disk drive 100 of FIG. 1 , the read head 211 of FIG. 2 , or othersuitable magnetic media drives.

The sensor 404 comprises the stack 400 of FIG. 4A disposed at a MFS.Thus, the sensor 404 comprises a first shield 410 a, a seed layer 412disposed over and in contact with the first shield 410 a, an SOT device417 disposed over and in contact with the seed layer 412, an MTJstructure 418 disposed over and in contact with the SOT device 417, acapping layer 420 disposed over and in contact with the MTJ structure,and a second shield 410 b disposed over and in contact with the cappinglayer 410. However, here the pinning layer 418 c of the MTJ structure418 is shown as comprising multiple layers. The pinning layer 418 ccomprises a first pinning layer 428 a disposed over and in contact withthe insulation layer 418 b, a Ru layer 428 b disposed over and incontact with the first pinning layer 428 a, a second pinning layer 428 cdisposed over and in contact with the Ru layer 428 b, and a thirdpinning layer 428 d disposed over and in contact with the second pinninglayer 428 c.

The first pinning layer 428 a, the second pinning layer 428 c, and thethird pinning layer 428 d each comprises a ferromagnetic material suchas one or more layers of CoFe, Coir, NiFe, and CoFeX alloy wherein X=B,Ta, Re, or Ir. The first pinning layer 428 a, the Ru layer 428 b, andthe second pinning layer 428 c may have the same depth in thez-direction; however, the third pinning layer 428 d may have a greaterdepth in the z-direction.

The sensor 404 further comprises an antiferromagnetic (AFM) layer 424recessed from the MFS, and disposed adjacent to the SOT device 417, andadjacent to and in contact with at least a portion of the MTJ structure418. The AFM layer 424 comprises a single or multiple layers of PtMn,NiMn, IrMn, IrMnCr, CrMnPt, FeMn, other antiferromagnetic materials, orcombinations thereof. A first insulation layer 411 separates the AFMlayer 424 from the first shield 410 a, the SOT device 417, and at leasta portion of the MTJ structure 418.

The AFM layer 424 pins the magnetic moment of the pinning layer 418 c bycontacting the third pinning layer 428 d, which has a greater depth inthe z-direction than other layers of the MTJ structure 418. However, theAFM layer 424 does not need to be disposed within the stack to pin themagnetic moment. Instead, the AFM layer 424 can be recessed from thedevice's backside (i.e. not exposed to MFS). This is beneficial forreducing reader RG and improving linear resolution.

FIG. 4D illustrates a cross-section of sensor 406 according to oneembodiment. The sensor 406 is the same as the sensor 404 of FIG. 4C;however, the AFM layer 424 differs. In sensor 406, the AFM layer 424 hasa smaller thickness in the y-direction as compared to the AFM layer 424of FIG. 4C. As such, the AFM layer is disposed adjacent to the FL 418 a,the insulation layer 418 b, the first pinning layer 428 a, the Ru layer428 b, and the second pinning layer 528 c.

FIG. 4E illustrates a cross-section of sensor 408 according to oneembodiment. The sensor 408 is similar to the sensor 404 of FIG. 4C;however, the stack and the AFM layer 424 differ. In sensor 408, there isno third pinning layer 428 d, and the AFM layer 424 is disposed at theMFS. The AFM layer 424 is further disposed between the second pinninglayer 428 c and the capping layer 420.

FIG. 5A illustrates a BiSb based STO stack 500 according to oneembodiment. The stack 500 may be used in the read head of the disk drive100 of FIG. 1 , the read head 211 of FIG. 2 , or other suitable magneticmedia drives. The stack 500 is similar to the stack 400 of FIG. 4A;however, here the layers are in a different configuration.

Here, the stack 500 comprises the seed layer 412 disposed over and incontact with the first shield 410 a, a MTJ structure 518 disposed overand in contact with the seed layer, an SOT device 517 disposed over andin contact with the MTJ structure 518, the capping layer 420 disposedover and in contact with the SOT device 517, and the second shield 410 bis disposed over and in contact with the capping layer 420. Since theSOT device 517 is disposed over the MTJ structure 518, the SOT device517 comprises additional buffer layers as compared to the SOT device 417of FIGS. 4A-4E. Here, the SOT device 517 comprises a first buffer layer516 a disposed over and in contact with the FL 418 a, the BiSb layer 414is disposed over and in contact with the first buffer layer 516 a, and asecond buffer layer 516 b is disposed over and in contact with the BiSblayer 414. The first buffer and the second buffer layers 516 a, 516 bmay or may not comprise of the same material as the buffer layer 416 ofFIGS. 4A-4D.

FIGS. 5B-5E illustrate various views of a bottom pinned BiSb basedsensor according to various embodiments (compared with FIGS. 4B-4E whichshow a top pinned BiSb based sensor). FIG. 5B illustrates an MFS view ofa sensor 502 according to one embodiment. The sensor 502 is a BiSb basedSTO device. The sensor 502 may be used in the read head of the diskdrive 100 of FIG. 1 , the read head 211 of FIG. 2 , or other suitablemagnetic media drives.

The sensor 502 comprises a first shield 410 a, a seed layer 412 disposedadjacent to and in contact with the first shield 410 a, a MTJ structure518 disposed adjacent to and in contact with the seed layer 412, a firstbuffer layer 516 a disposed adjacent to and in contact with the MTJstructure 518, a BiSb layer 414 disposed adjacent to and in contact thefirst buffer layer 516 a, a second buffer layer 516 b disposed adjacentto and in contact with the BiSb layer 414, a capping layer 420 disposedadjacent to and in contact with the second buffer layer 516 b, and asecond shield 410 b, disposed adjacent to and in contact with thecapping layer 420.

The sensor further comprises a first bias 430 a, and a second bias 430b, wherein the first and second bias 430 a, 430 b, are disposed adjacentto the MTJ structure 418 and the first buffer layer 516 a, wherein afirst insulation layer 415 a separates the first bias 430 a from the MTJstructure 518 and the first buffer layer 516 a, and a second insulationlayer 415 b separates the second bias 430 b and the MTJ structure 518and the first buffer layer 516 a (i.e. the MTJ structure 518 and thefirst buffer layer 516 a are disposed between the first and second bias430 a, 430 b in the x-direction). The first and second bias 430 a, 430 bare further disposed in between the seed layer 412 and the BiSb layer414 in the y-direction. In some embodiments, the first and second bias430 a, 430 b are disposed in contact with the seed layer 412, as shown.In some embodiments, first insulation layer 415 a further insulates thefirst bias 430 a from the seed layer 412, and the second insulationlayer 415 b insulates the second bias 430 b from the seed layer 412(i.e. the first and second bias 430 a, 430 b do not contact the seedlayer 412).

The first shield 410 a, the seed layer 412, the MTJ structure 518, thefirst buffer layer 516 a, the first bias 430 a, the second bias 430 b,the BiSb layer 414, the second buffer layer 516 b, the capping layer420, and the second shield 410 b, may be comprised of the same materialsas for the corresponding layers as described in FIGS. 4A-4E. Inparticular, the first buffer layer 516 a and the second buffer layer 516b may be comprised of the same materials as for the buffer layer 416.

FIG. 5C illustrates a cross-sectional side view of a sensor 504according to one embodiment. The sensor 504 is similar to sensor 404 ofFIG. 4C; however, here the sensor 504 is bottom pinned BiSb based STOdevice. The sensor 504 may be sensor 502 of FIG. 5B. The sensor 504 maybe used in the read head of the disk drive 100 of FIG. 1 , the read head211 of FIG. 2 , or other suitable magnetic media drives.

The sensor 504 comprises the stack 500 of FIG. 5A, wherein the stack isdisposed at a MFS. Thus, the sensor 504 comprises the first shield 410a, the seed layer 412 disposed over and in contact with the first shield410 a, the MTJ structure 518 disposed over and in contact with the seedlayer 412, the SOT device 517 disposed over and in contact with the MTJstructure 518, the capping layer 420 disposed over and in contact withthe SOT device 517, and the second shield 410 b disposed over and incontact with the capping layer 420. However, here the pinning layer 518c of the MTJ structure 518 is shown as comprising three layers ratherthan two layers in comparison to FIG. 4C. The pinning layer 518 ccomprises the first pinning layer 428 a over and in contact with theseed layer 412, the Ru layer 428 b disposed over and in contact with thefirst pinning layer 428 a, and the second pinning layer 428 c disposedbetween the Ru layer 428 b and the insulating layer 418 b.

Similar to sensor 404 of FIG. 4C, the sensor 504 further comprises theantiferromagnetic (AFM) layer 424 recessed from the MFS. The AFM layer424 is disposed adjacent to the SOT device 517, and adjacent to and incontact with at least a portion of the MTJ structure 518. The firstinsulation layer 411 separates the AFM layer 424 from at least a portionof the MTJ structure 518, the SOT device 517, and the capping layer 420.

The AFM layer 424 pins the magnetic moment of the pinning layer 518 c.However, the AFM layer 424 does not need to be disposed within the stackto pin the magnetic moment. Instead, the AFM layer 424 can be recessedfrom the device's backside (i.e. not exposed to MFS). This is beneficialfor reducing reader (read gap) RG and improving linear resolution.

FIG. 5D illustrates a cross-sectional side view of a sensor 506according to one embodiment. The sensor 506 is the same as the sensor504 of FIG. 5C; however, the thickness of the AFM layer 424 differs. Insensor 506, the AFM layer 424 has a smaller thickness in the y-directionas compared to the AFM layer 424 of FIG. 5C. As such, the AFM layer isdisposed adjacent to the MTJ structure 518, but is not adjacent to theSOT device 517.

FIG. 5E illustrates a cross-section of sensor 508 according to oneembodiment. The sensor 508 is the same as the sensor 504 of FIG. 5C;however, the AFM layer 424 differs. In sensor 508, the AFM layer 424 isdisposed at the MFS, and further disposed between the seed layer 412 andthe first shield 410 a.

It is to be understood that although the various layers described inFIGS. 4A-4E and 5A-5E may be depicted as being a certain depth, width,or thickness, this is not to be considered limiting, but merely forillustrative purposes. For example, in FIGS. 4C and 4D, although thefirst and second shields 410 a, 410 b are shown as being the same depthin the z-direction as the third pinning layer 428 d and the cappinglayer 420, the first and second shields 410 a, 410 b may be much largerthan the other layers of the sensor 404. Thus, unless specificallydescribed the layers FIGS. 4A-4E and 5A-5E may be larger or smallerdepending on the embodiment.

It is to be understood that the above embodiments, are merely examplesof configurations of sensors, and the sensors may comprise more or lesslayers depending on the embodiment.

As discussed above in FIGS. 3A and 3B, because the signal output isdetected at the frequency domain, the resistance across the sensor doesnot significantly impact the noise. Thus, the sensor signal to noiseratio (SNR) can be improved by using a MTJ structure with a higherresistance per area, such as the MTJ structures 418 and 518 described inFIGS. 4A-4E and 5A-5E, which will produce a higher tunnelmagnetoresistance (TMR) ratio to achieve a higher signal withoutsuffering higher noise. Thus, by utilizing a BiSb layer as a topologicalinsulator in a SOT-based STO device, the spin Hall angle can beincreased, thereby improving the spin torque efficiency and reliabilityof the STO device.

In one embodiment, a sensor, comprising: a seed layer; a bismuthantimony (BiSb) layer disposed over the seed layer; a buffer layerdisposed over the BiSb layer; a magnetic tunnel junction (MTJ) structuredisposed over the buffer layer, wherein the seed layer, the BiSb layer,the buffer layer, and the MTJ structure are disposed at a media facingsurface (MFS); and an antiferromagnetic (AFM) layer.

The BiSb layer has a (012) orientation. The AFM layer is recessed fromthe MFS. The sensor, wherein the AFM layer contacts at least a portionof the MTJ structure. The sensor, wherein the AFM layer disposed at theMFS and adjacent to the seed layer. A magnetic recording head comprisingthe sensor is also disclosed wherein magnetic recording head comprises afirst shield and a second shield. The sensor is disposed between thefirst shield and the second shield; the BiSb layer is spaced a firstdistance from the first shield, and spaced a second distance from thesecond shield, wherein the first distance and the second distance aredifferent; and the AFM layer is spaced a third distance from the firstshield, and spaced a fourth distance from the second shield. The thirddistance and the fourth distance are different. The first distance andthe third distance are different. A magnetic recording device comprisingthe magnetic recording head is also disclosed. The magnetic recordingdevice comprises a magnetic recording media; the magnetic recordinghead; and a control unit configured to: flow current through the bismuthantimony (BiSb) layer while reading data from the magnetic recordingmedia; and measure frequency of a precession of a free layer in thesensor, wherein the precession is responsive to a magnetic fieldgenerated by the magnetic recording media.

In another embodiment, a sensor, comprising: a seed layer; a magnetictunnel junction (MTJ) structure disposed over the seed layer; a firstbuffer layer disposed over the MTJ structure; a bismuth antimony (BiSb)layer disposed over the first buffer layer; a second buffer layerdisposed over the BiSb layer; a capping layer disposed over the secondbuffer layer; wherein the seed layer, the MTJ structure, the firstbuffer layer, the BiSb layer, the second buffer layer, and the cappinglayer are disposed at a media facing surface (MFS); and anantiferromagnetic (AFM) layer, wherein the AFM is disposed between theseed layer and the capping layer.

The AFM layer is disposed at the MFS adjacent the MTJ structure. The AFMlayer and a free layer of the MTJ structure are at least partiallyaligned in a direction perpendicular to the MFS. The AFM layer and afree layer of the MTJ structure are not aligned in a directionperpendicular to the MFS. A magnetic recording head comprising thesensor is also disclosed as is a magnetic recording device comprisingthe magnetic recording head. The magnetic recording device comprises amagnetic recording media; the magnetic recording head; and a controlunit configured to: flow current through the bismuth antimony (BiSb)layer while reading data from the magnetic recording media; and measurefrequency of a precession of a free layer in the sensor, wherein theprecession is responsive to a magnetic field generated by the magneticrecording media.

In yet another embodiment, a sensor comprises: a bismuth antimony (BiSb)layer having a (012) orientation; a free layer; an MgO layer; a pinninglayer; a capping layer; an antiferromagnetic (AFM) layer; and a biaslayer disposed at a media facing surface (MFS).

A magnetic recording head comprising the sensor is also disclosed wherethe magnetic recording head comprises: a first shield; and a secondshield, wherein the bias layer is disposed between the BiSb layer andthe second shield. A magnetic recording device comprising the magneticrecording head is also disclosed. The magnetic recording devicecomprises a magnetic recording media; the magnetic recording head; and acontrol unit configured to: flow current through the bismuth antimony(BiSb) layer while reading data from the magnetic recording media; andmeasure frequency of a precession of a free layer in the sensor, whereinthe precession is responsive to a magnetic field generated by themagnetic recording media.

In another embodiment, a method of using a magnetic recording headcomprises: flowing a current through a spin orbit torque (SOT) device ofa spin torque oscillator (STO) sensor while reading data from a magneticrecording media; and measuring frequency of a precession of the a freelayer in the STO sensor, wherein the precession is responsive to amagnetic field generated by the magnetic recording media. The SOT devicehas a spin Hall angle of 2 or more. The SOT device is disposed in a readhead of the magnetic recording head. The current is flowed in-planeinside a BiSb layer of the SOT device. The method further includesflowing a small sensing current perpendicular to a plane of the magneticrecording media, wherein a signal is read out by the measuring. There isa linear relationship between the measured frequency and an appliedmagnetic field. The method further comprises detecting a bit recorded onthe magnetic recording media based upon the measured frequency.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A sensor, comprising: a seed layer; a bismuthantimony (BiSb) layer disposed over the seed layer; a buffer layerdisposed over the BiSb layer; a magnetic tunnel junction (MTJ) structuredisposed over the buffer layer, wherein the seed layer, the BiSb layer,the buffer layer, and the MTJ structure are disposed at a media facingsurface (MFS); and an antiferromagnetic (AFM) layer.
 2. The sensor ofclaim 1, wherein the BiSb layer has a (012) orientation.
 3. The sensorof claim 1, wherein the AFM layer is recessed from the MFS.
 4. Thesensor of claim 1, wherein the AFM layer contacts at least a portion ofthe MTJ structure.
 5. The sensor of claim 1, wherein the AFM layer isdisposed at the MFS and adjacent the seed layer.
 6. A magnetic recordinghead comprising the sensor of claim
 1. 7. The magnetic recording head ofclaim 6, further comprising a first shield and a second shield, wherein:the sensor is disposed between the first shield and the second shield;the BiSb layer is spaced a first distance from the first shield, andspaced a second distance from the second shield, wherein the firstdistance and the second distance are different; and the AFM layer isspaced a third distance from the first shield, and spaced a fourthdistance from the second shield.
 8. The magnetic recording head of claim7, wherein the third distance and the fourth distance are different. 9.The magnetic recording head of claim 7, wherein the first distance andthe third distance are different.
 10. A magnetic recording device,comprising: a magnetic recording media; the magnetic recording head ofclaim 6; and a control unit configured to: flow current through thebismuth antimony (BiSb) layer while reading data from the magneticrecording media; and measure frequency of a precession of a free layerin the sensor, wherein the precession is responsive to a magnetic fieldgenerated by the magnetic recording media.
 11. A sensor, comprising: abismuth antimony (BiSb) layer having a (012) orientation; a free layerdisposed over the BiSb layer; an MgO layer disposed over the free layer;a pinning layer disposed directly over the MgO layer; a capping layerdisposed over the pinning layer; an antiferromagnetic (AFM) layer; and abias layer disposed at a media facing surface (MFS).
 12. The sensor ofclaim 11, wherein the AFM layer is disposed between the pinning layerand the cap layer at the MFS.
 13. The sensor of claim 11, wherein theAFM layer is recessed from the MFS.
 14. The sensor of claim 11, furthercomprising a buffer layer disposed between the BiSb layer and the freelayer.
 15. The sensor of claim 11, wherein the MgO layer is disposed incontact with the free layer.
 16. A magnetic recording head comprisingthe sensor of claim
 11. 17. The magnetic recording head of claim 16further comprising: a first shield; and a second shield, wherein thebias layer is disposed between the BiSb layer and the second shield. 18.A magnetic recording device, comprising: a magnetic recording media; themagnetic recording head of claim 16; and a control unit configured to:flow current through the bismuth antimony (BiSb) layer while readingdata from the magnetic recording media; and measure frequency of aprecession of the free layer in the sensor, wherein the precession isresponsive to a magnetic field generated by the magnetic recordingmedia.
 19. A sensor, comprising: a seed layer disposed at a media facingsurface (MFS); a bismuth antimony (BiSb) layer having a (012)orientation disposed on and in contact with the seed layer, the BiSblayer being disposed at the MFS; a buffer layer disposed on and incontact with the BiSb layer; a free layer disposed over the bufferlayer; a first pinning layer disposed over the free layer; an Ru layerdisposed over the first pinning layer; and an antiferromagnetic (AFM)layer.
 20. The sensor of claim 19, further comprising a second pinninglayer disposed over the Ru layer.
 21. The sensor of claim 20, whereinthe AFM layer is disposed on the second pinning layer, the AFM layerbeing disposed at the MFS.
 22. The sensor of claim 20, wherein the freelayer, the first pinning layer, the Ru layer, and the second pinninglayer form a magnetic tunnel junction (MTJ) structure.
 23. The sensor ofclaim 19, further comprising: an insulating layer disposed between thefree layer and the first pinning layer; and a capping layer disposedover the Ru layer.
 24. The sensor of claim 19, wherein the AFM layer isrecessed from the MFS.
 25. A magnetic recording head comprising thesensor of claim
 19. 26. The magnetic recording head of claim 25, furthercomprising: a first shield; and a second shield, wherein the sensor isdisposed between the first shield and the second shield.
 27. A magneticrecording device, comprising: a magnetic recording media; the magneticrecording head of claim 26; and a control unit configured to: flowcurrent through the BiSb layer while reading data from the magneticrecording media; and measure frequency of a precession of the free layerin the sensor, wherein the precession is responsive to a magnetic fieldgenerated by the magnetic recording media.